The present invention finds application to cellular communications and relates to mobile terminal responses to pages in a mobile communications system.
A cellular telephone is one example of what is generally characterized as a xe2x80x9cmobile stationxe2x80x9d (MS), a xe2x80x9cmobile terminalxe2x80x9d (MT), or even more generally as xe2x80x9cuser equipmentxe2x80x9d (UE). The term mobile terminal is employed hereafter for purposes of description. Telecommunications services are provided between a cellular telecommunications network and a mobile terminal over an air interface, e.g., over radio frequencies. An active mobile terminal communicates over the air interface with one or more base stations. The base stations are managed by base station controllers (BSCs), which in some systems, are known as radio network controllers (RNCs). The term RNC is employed hereafter for purposes of description. Radio network controllers are coupled to one or more telecommunications networks by way of one or more control nodes such as a mobile switching center (MSC) node for connecting to connection-oriented, circuit-switched networks such as PSTN and/or ISDN, and a general packet radio service.(e.g., GPRS) node for connecting to connectionless, packet-switched networks such as the Internet.
A simplified cellular communications system is shown in function block format in FIG. 1. An example core network is connected to several radio network controllers (RNC) including RNC1, RNC2, and RNC3. Each RNC controls the allocation of radio resources and radio connectivity operations for a set of cells: RNC1 controls cells 1:1-1:5, RNC2 controls cells 2:1-2:5, and RNC3 controls cells 3:1-3:5. The RNCs communicate by way of a signaling network, e.g., signaling system number 7 (SS7), and a transport network. Each cell is a geographical area where radio coverage is provided by radio base station equipment at the base station site. A base station may serve one or more cells. A xe2x80x9chandoverxe2x80x9d occurs as a mobile terminal travels from an old cell to a new cell which permits mobile terminals to xe2x80x9croamxe2x80x9d considerable distances. Each cell is identified using a unique identity broadcast in that cell over a common broadcast channel.
As indicated in FIG. 1, the RNCs, the interconnecting signaling and transport network, and the radio base station equipment in each of the cells together comprise a radio access network (RAN). Mobile terminals (MTs) permit a subscriber access to telecommunications services offered by the core network via the RAN. The radio access network controls radio connections and transmissions between the core network and the mobile terminals.
Different roles may be assigned to RNCs in the RAN depending on circumstances, configurations, etc. One RNC role is that of a xe2x80x9ccontrollingxe2x80x9d RNC (CRNC) which controls the radio resources in its set of cells. In the example shown in FIG. 1, the RNC1 is the controlling RNC for cells 1:1 to 1:5, the RNC2 is the controlling RNC for cells 2:1 to 2:5, and the RNC3 is the controlling RNC for cells 3:1 to 3:5.
FIG. 2 shows adjacent cells in a cellular communications network. An active cell denotes the cell currently supporting a radio connection with a mobile terminal. Adjacent neighboring cells may be selected by the mobile terminal via forward handover to support the connection. Forward handover or cell reselection is a process where a mobile terminal itself continues an established connection between a core network and the mobile terminal as the mobile terminal moves between different cells in the radio access network. Contrasted with traditional handover, the mobile terminal in forward handover independently re-establishes the radio connection with a new cell. This re-establishment of the connection is performed without prior notification via the old cell. Nor is there advance preparation in the network to continue the communication via the new cell. It is the mobile terminal that initiates and orchestrates forward handover rather than the core network, the core network node (e.g., an MSC), or the radio access network (RAN).
FIG. 3 illustrates an example where cells controlled by RNC1-RNC3 are grouped into registration areas, RA1-RA6, each consisting of one or several cells. Information transmitted on the broadcast channel in each cell may contain cell and registration area identifiers for purposes of registration control. As long as such cell and registration area identifiers broadcast by a specific cell contain the same cell and registration area identifiers assigned to the mobile terminal during the most recent cell or RA update procedure, the mobile terminal need not register. However, when the terminal mobile terminal does not recognize the broadcast cell and registration area identifiers in the cell, it initiates an RA update procedure.
To reach a mobile terminal, the radio network initiates a paging procedure. More specifically, a paging message containing the mobile terminal identity is transmit on a paging channel. In order for the paging message to be directed to an area where the mobile terminal is located, the radio network stores in memory, determines the current location of the mobile station either on a cell level, on a registration area level, or on some other level. The page is then transmitted in a paging area which may, for example (although not necessarily), be identical to the registration cell or a registration area. Another example paging area may correspond to cells 1:1-1:5 associated with RNC1 as shown in FIG.1.
When the mobile terminal listens to the paging channel in its current cell, it may be decide to change to another cell using a cell reselection process as a result of changed radio conditions. More specifically, another cell may have better, current radio conditions for communication for that mobile terminal. The cell reselection may be decided based on one or more cell selection evaluation criteria. For example in a CDMA based system, the mobile terminal listening for pages need only be concerned about the quality of the downlink transmission from the base station in the current cell. On the other hand, if the mobile terminal must respond to the page, it must consider the uplink radio conditions over which it must transmit in that cell. The uplink conditions may not be optimal, meaning that the mobile would have to transmit at a higher power than it would from a more optimal cell. In this example, the mobile may select the more optimum cell before it transmits a response to the page. If the mobile terminal changes its current cell, the new cell may belong to a new registration area. Normally, this would trigger a registration procedure.
Balancing the desire to select the most optimal cell, e.g., to find and select the cell with the best uplink and downlink radio conditions, is the need to conserve battery power of the mobile terminal. Therefore, the mobile terminal may limit cell selection evaluation to certain time periods such as only when the mobile terminal is listening to the paging channel. Otherwise, the mobile terminal must use precious battery power to perform the cell reselection evaluation process at another time separate from the time it is powered up to listen to the paging channel.
The mobile terminal responds to a page by sending a paging response message to the radio network. Traditionally, the mobile terminal responds to the paging message in the same cell where it received that paging message. However, because the mobile terminal is listening to the paging channel, it may also be evaluating whether the current cell is the optimum cell, e.g., for uplink transmission in response to the page in a CDMA-based system, before responding to the page. If the mobile terminal happens to select another, more optimum cell and send a paging response message to that new cell, that message may not be routed to the paging originator. For example, if the newly selected cell belongs to a different RNC than the RNC that originated the page, the paging response may not find its way back to the page originating RNC or the page originating, external core network. Furthermore, the new cell might belong to another network operator, or even another type of cellular system, e.g., GSM instead of wideband CDMA. The result is a significant number of xe2x80x9cunsolicitedxe2x80x9d paging responses that are not recognized by the receiving radio network control node, and therefore, are not directed to the paging originator. In second generation mobile communication systems, such as GSM, this situation is avoided by prohibiting a mobile terminal from responding to a page from a cell outside the registration area where it is registered. But this prohibition greatly restricts the flexibility and coverage area of the radio network.
It is similarly possible to constrain the mobile terminal so that it only responds to the page in the cell where it received the page. However, the mobile terminal may be forced to remain on a non-optimal cell with poor radio conditions, possibly resulting in erroneously received or transmitted messages. The mobile terminal would need to monitor the uplink and downlink conditions of its current and neighboring cells to determine and select the optimum cell at times other than when receiving a page. This may be acceptable if such evaluations occur frequently, but at the cost of increased battery loss at the mobile terminal resulting from those frequent evaluations. Furthermore, even with increased evaluation periods, the radio conditions may be changing rapidly so that there is a possibility that the radio conditions may have changed for the worse by the time the mobile terminal is listening/responding to a page.
The present invention solves these problems by providing a mechanism to efficiently and reliably route a paging response from a mobile terminal to the page originatorxe2x80x94even if the mobile terminal has selected a new, more optimum cell just before responding to the page. As a result, the cell evaluation and selection process need only be performed while the mobile is listening to the paging channel, thereby saving mobile terminal battery life. Since the mobile terminal checks for the optimum cell just before it transmits a paging response, there is less chance of increased interference caused by the uplink transmission, of a lost connection, or of an error in the message.
A paging origination identifier is associated with an origination of a page to a mobile radio terminal. The mobile terminal responds to the page using the identifier. For example, assuming that the page to the mobile terminal is in a first area, the mobile terminal responds to the page from a second area and includes the identifier in that response. The paging response may be part of an initial random access message or included with a paging access message sent by the mobile terminal after a connection is made with the radio network. The identifier is used to route the page response through the radio network ultimately to the paging originator. Various example routing embodiments using the identifier in a paging response from the mobile terminal are described below. The identifier may be for example a paging area identifier, a registration area identifier, or a network exchange identifier and may be included in the page. Alternatively, the identifier need not be included with the page. An example identifier in this situation is the cell identity where the mobile terminal received the page.